Something else to consider: chocolate cake has sugar which will make the blood glucose levels rise. It could give someone enough extra energy and clear up the thought process enough to offset the loss of bishops and give them a better opportunity to win.
On the other hand, wooden bishops are extremely high in fiber, which could unblock someone and help them think more clearly. Although the treament of wood (paint, laquer, stain, rot or fire retardant, etc... might be toxic). Bishops made of other materials could have other advantages or disadvantages. For example, bishops made of stone or granite might offer important minerals, but be hard on the teeth, necessitating other means of breaking them down for consumption. To get the maximum value from eating a wooden bishop directly, one would have to chew very carefully and it would take a long time to accomplish, and then a long while afterwards to see any benefit.
So in that regard I think cake offers some clear benefit, unless the fats in the cake lead to a heart attack or stroke. There are vegan variations that are low fat, or at least higher in healthier fats.
I think the nutritional tradeoffs are an area that need more study. If people would like to submit various samples of cake to review, we could get an institution going to evaluate them.
Re: making a bishop vs making a delicious chocolate cake
I can just imagine a Bishop and it's there. I can imagine an entire game of chess and it exists.
If I try imagining a chocolate cake, I just make myself hungry for the real thing.
It's far easier to make a Bishop than a piece of cake.